Method for the production of thermographic copies from an electrostatic powder image



April 1966 K F. DE TROEYER ETAL 3,246,148

METHOD FOII THE PRODUCTION OF THERMOGRAPHIC COPIES FROM AN ELECTROSTATIC POWDER IMAGE Flled March 28, 1963 2 Sheets-Sheet 1 L A B --D C -D D E l l FORMAT/0N DEVELOPMENT TRANSFER HEAT-co- REMovAL OF OF THE OF THE OF THE PY/NG OF THE POWDER LA TENT LATENT PowoER THE POW- l IMAGE ELEGTRO- ELECTRO- IMAGE To DER IMAGE STAT/c sTATIc AN INTER- I I IMAGE IMAGE WITH MED/ATE POWDER SUPPORT I" J F G I AFTER-rIrE/ITMEIIT m Of/[LWLA' 72-7/7' TI/EF/Vfl6/D1P/I/6I/VA6E INVENTORS KAREL FRANS DE TROEYER JOZEF LEONARD. VAN ENGELAND ROBERT JOSEPH NOE WATSON, COLE GR/NDLE 8 WATSON ATTORNEYS Apnfi 12, 1966 K. F. DE TROEYER ETAL 3,245,148

METHOD FOR THE PRODUCTION OF THERMOGRAPHIC COPIES FROM AN ELECTROSTATIC POWDER IMAGE Filed March 28, 1963 2 Sheets-Sheet 2 30 24 u, 29 23 :4, WE fig INVENTORS KAREL FRANS DE TROEYER JOZEF LEONARD VAN ENGELAND ROBERT JOSEPH NOE BY WATSON, COLE, GR/NDLE & WA TSON ATTORNEYS United States Patent METHOD FOR THE PRQDUfZTIDN 0F THERMO- GRAPHIC CBPKES FROM AN ELEQTRQSTATIC REV/DER IMAGE Karel Frans De Troeyer, Antwerp, Jozef Leonard Van Engeland, St. Kateliine-Waver, and Robert Joseph Noe, Eerchem-Antwerp, Belgium, assignors to Gevaert Photo-Producten N.V., Mortsel-Antwerp, Belgium, 2! Belgian company Filed Mar. 28, 1963, Ser. No. 268,779 Claims priority, application Belgium, Mar. 30, 1962, 41,518, Patent 615,804 8 Claims. (til. 250-65) The present invention relates to a method for the production of thermographic copies.

It is known to obtain copies of an original in applying a thermal copying method according to which a heat-sensitive sheet material is used which on exceeding a critical temperature undergoes a physical or chemical change. This change becomes visible, either immediately or after a physical and/or chemical after-treatment. The heatsensitive or thermographic sheet material is brought into contact with the original and submitted to a short intense infra-red radiation. On these image areas of the original which absorb more infra-red radiation than the background, said radiation is converted into heat. When by this heat a critical temperature is exceeded in the heatsensitive sheet a physical or chemical reaction is initiated in those areas, which correspond to the infra-red absorbing image areas. Such methods and/or materials are among others described in the French patent specifications 1,288,059 and 1,231,903, and in the United States Patent 2,740,896.

These very simple reproduction methods have the important disadvantage to reproduce very insufficiently those image areas of the original which absorb insufiiciently infra-red light. For this reason, originals or prints obtained with organic dye-stuffs such as aniline dyestuffs which are used, e.g., in the preparation of ink for ink-pads, ink for fountain pens and ink for ball point pens or similar marking means, cannot be recorded by thermography.

It is therefor the object of the present invention to overcome this disadvantage. The method according to the present invention comprises first producing a powder image of the original to be copies by means of an infra-red absorbing non-thermoplastic powder and next making a thermographic copy of this powder image.

More particularly, it is an object of the present invention to provide a method for the production of thermographic copies, comprising the steps of forming on a recording material a powder image in conformity with the image or pattern to be reproduced by means of an infra-red absorbing, non-thermoplastic powder, contacting the recording material carrying the powder image with a thermosensitive material, being essentially less infra-red absorbing as the said powder, exposing the contacted materials to infra-red radiation, creating thereby a physical or chemical change in correspondence with the powder image in said thermosensitive material.

According to an interesting embodiment of the method of the present invention first an eletcrostatic latent image of an original, which cannot directly thermographically ice be reproduced, is formed in a photoconductive layer according to an electrophotographic method, then said latent image is developed by menas of an infra-red absorbing non-thermoplastic powder, where after by infra-red radiation in a thermosensitive layer a thermographic copy of this powder image is produced.

- This method solves the problem of reproducing colors by thermography, since it is possible by using appropriate photoconductive substances, either in the presence of sensitizers or not, as needed, to extend the sensitivity of the photoconductive layer all over the entire visible spectrum.

With regard to the usual electrophotographic methods according to which the latent electrostatic image is developed with powder which has to be fixed, e.g., by heat or by organic solvents, the present method shows the advantage that the developing powder need not be fixed and can be recovered.

The electrostatically attracted powder image need not necessarily to be formed according to an electrophotographic process but can also be produced in conformity with an electrostatic image which is formed by the imagewise or signal-wise charging an insulating recording material.

It is to be especially understood that the scope of the present invention is not limited to a thermographic method wherein a powder image is formed by means of an electrostatic charge pattern, but embraces the use of magnetic patterns for development with a suitable magnetic powder to form an infra-red absorbing powder image which can thermographically be reproduced.

Thus, the present invention is not confined to the use of any particular powder provided the latter is infra-red absorbing and non-thermoplastic.

As to the thermosensitive recording material, it is obvious to prefer for purposes of the present method, a thermosensitive recording material which is substantially less infra-red absorbing than the infra-red absorbing developing powder.

The composition of some thermosensitive layers for use in the present invention is given hereinafter in the description.

In lieu of a thermosensitive material in which a visible physical or chemical change is created by exposure to heat a material such .as described in the French patent specification 1,288,059 can also be used. At a critical temperature, this material becomes conductive so that an invisible electrostatic charge pattern can be formed by image-wise heating the material either while carrying a previously applied uniform charge or with a uniform charge being applied during or immediately thereafter. Further, the electrostatic latent image obtained on this thermosensitive material can be developed according to a known method with a developing material which can be fixed. Particulars concerning this embodiment are given in Example 5.

Different embodiments of the present invention are described in the examples and illustrated by the corresponding drawings.

FIG. 1 is a schematic view of the successive steps performed in carrying out the process of the present invention.

FIGS. 2-4, 4a, 5 and6 show diflerent embodiments of the thermographic copying method of" an electrostatic powder image.

FIG. 7 is an automatic copy in apparatus with optical exposing.

FIG. 8 shows the copying method of a magnetic powder image.

FIG. 9 illustrates the method for preparing a duplicating master.-

FIG. 10 is a diagrammatic view similar to FIGS. 26 and illustrating a further embodiment of the method of this invention.

In FIGURE 1, A represents the formation on a recording material of a latent image or pattern, which can be developed with an infra-red absorbing powder, B represents. the step of rendering visible. the latent image by mans of said powder, C shows the optional step of transferring the powder image onto another support, D represents the thermographic copying of: the. powder image andE is the removal of the infra-red absorbing powder from the recording material, if not to be fixed or already transferred.

In step A .a latent image is formed which can be developed with powder.

Instead of producing the. thermographic copy directly as in step D above, step D can result in the formation of a latent thermographic image which can subsequently be developed to. a visible image. by an appropriate aftertreatment. This optional step is indicated by dotted lines in the schematic diagram of FIG. 1.

According to the best-known electrophotographic method, a latent electrostatic image, which can be developed with electrostatically attractable powder, is formed on a photoconductiv'elayer by first unifromly electrostatically charging said layer, e.g., by rubbing with a soft material or with a material possessing a high electric resistivity, e.g., by rubbing with a cylinder coated with polystyrene, bycorona discharge, by contact charging or by the discharge of a condenser, and thereupon by exposing said charged photoconductive layer to an original.

According to a known magnetic recording method a magnetisable layer is signal-wise or image-wise magnetized, thus producing a magnetic pattern which can be made visible with a magnetic or magnetisable powder.

The latent image or pattern is then developed, i.e., made visible inthe step B. This development isexecuted according to generally known techniques wherein use, is made of the magnetic and/or electrostatic attraction or repellency of finely divided substances which are present in a powder or in a powder mixture, in an electrically insulating liquid, e.g., as a suspension, or in a gas, e.g., as aerosol. By an appropriate choice of the sign of the charge of the developing powder a negative or positive powder image of the original can be obtained. So, when the statement is made in this description that a negative as well as a positive powder image of the original can be formed, it is to be understood, irrespective of type, the powder image is always in conformity with the original produced. If the photoconductive layer and the developing powder have the same charge sign, then the powder only adheres on the discharged areas, i.e., on the exposed areas, and a powder image is obtained having a gradation curve parallel to the gradation curve of the original (a positive image). If the photoconductive layer and the developing powder have an op posite sign, the powder only adheres to the charged areas, i.e., on the unexposed areas, and then a powder image is obtained having a gradation curve opposite to the gradation curve of the original (a negative image).

The transfer of the powder image from the recording layer to an intermediate support, if practiced, occurs in step C. This step is not necessary for the performance, in principle, of the method according to the invention. In some circumstances, however, which are further explained in the description, it is advantageous to transfer the powder image from the recording layer to an intermediate support before copying.

In step D the powder image is copied in a thermographic way as well known in the art.

'Finally, in step E the recording material is freed from the infra-red absorbing powder, e.g., by brushing off, sucking oif, shaking off, or by blowing off. In case the powder is a magnetic substance, it can also be removed by means of a magnet but then the original magnetic pattern is, of course, also erased.

FIG. 2 represents an embodiment wherein the recording material, which includes a recording layer 1 (in the present case a practically non-infra-red absorbing photoconductive layer present on an electrically conductive support 2) and a powder image 3 formed on layer 1 from an infra-red absorbing non-thermoplastic powder, is contacted with a thermosensitive material consisting of a support 4 and a thermosensitive layer 5. According to this embodiment, the support 4 is pressed against the powder image 3. By a short intense infra-red radiation of the two materials pressed against each other, a visible thermographic copy 6 of the powder image 3 is produced in the thermosensitive layer 5. As to the methods illustrated in the drawings, the radiation can be applied either to the side of the photoconductive layer or to the side of the thermosensitive copying sheet. After removal of the powder 3, the recording layer can be used again. It is evident that the powder image is allowed to remain on the recording layer if more thermographic copies of the same powder image are to be obtained.

FIG. 3 illustrates also the thermographic copying onto a separate thermosensitive sheet with the difference that the thermosensitive layer 5 is adjacent to the powder image 3. In this way a laterally reversed image of the powder image is obtained.

FIG. 4 illustrates an embodiment using a recording material bearing a thermosensitive layer 5 at one side of a support 2and a photoconductive recording layer 1 at the other side of the same support.

In the latter case the image 6 thermographically formed in the layer 5 is a copy of the powder image 3.

FIG. 4a represents a variation of the embodiment of FIG. 4 in which the powder image 3 is formed directly on the thermosensitive layer 5 of the composite recording material, the material then being exposed to infra-red radiation to create the image 6 in the thermosensitive layer.

FIG. 5 illustrates an embodiment wherein an electrophotographic material, consisting of a photoconductive layer. 1, on which a powder image 3 has been formed, and the support 2, is contacted with a thermosensitive material consisting of a suitable fusible dyestuif containing layer 5 on a support 4 in such a way that the rear side of support 2 is facing the thermosensitive material. After infra-red irradiation and separation of the materials. a laterally reversed color image 6 on the rear side of the electrophotographic support 2 is obtained in conformity with the powder image 3 on the photoconductive record ing layer 1.

The recording material bearing the color pattern can be used as a hectographic duplicating master in an alcohol duplicator and several copies are obtained therewith. It is evident that a color coupler instead of a dyestufi' can be incorporated into the fusible layer so that a dyestuif can be formed therein by an after-treatment.

'FIG. 6 ilustrates the thermographic copying of a transferred powder image 3. The powder image is transferred from the recording layer 1 to a receiving sheet 4 bearing a thermosensitive layer 5. The powder image 3 is exposed to infra-red radiation whereby the thermographic copy 6 is produced.

This latter embodiment shows the advantage that for the thermographic copying one does not depend on the choice of photoconductive substances which are practically non-infra-red absorbing. This is very important since,

thereby the disadvantage of an insuificiently selective heating of the developing powder, among other reasons due to the strongly infra-red absorbing character of the recording layer such as, e.g., selenium or iron oxide, is avoided. The result of an insufficiently selective heating of the powder image is the coloring of the image background in the thermosensitive sheet. When the powder image of the recording sheet is first transferred to a receiving sheet showing a very small infra-red absorption, then the attainable selectivity will be much higher.

For the transfer of the powder image, the known methods can be applied, e.g., electrostatic transfer, magnetic transfer and transfer by wetting of the receiving sheet. Embodiments of these techniques are respectively described in the United States Patents 2,297,691 and 2,684,901 and the German patent specification 969,593.

FIG. 7 illustrates a device for performing the method of the present invention wherein use is made of a powder image obtained by electrophotography.

In this device an electrophotographic mate-rial 7 is used consisting of an aluminum support and a photoconductive layer, which contains photoconductive zinc oxide dispersed in a binding agent. The support forms an endless belt which is moved on the earthened guide rollers 8, 9, 10 and 11. The photoconductive layer, lying at the outside, is charged by a corona charging device 1-2. During the short stopping of said belt an electrostatic latent image of the original is formed by exposure in using a projection system 13. The powder development of the electrostatic latent image is done by the device 14.

The thermographic copying of the powder image is done by means of an infra-red radiation source 15. A thermographic sheet 16, fed from a supply roll 17 and in which, upon exceeding a critical temperature, a chemical or physical reaction is created, is pressed by means of the rollers 18 against the belt 17 at the place where the-belt 7 contacts the roller 10. The radiation by means of the infra-red source forces the temperature in the sheet 16 to exceed the critical value at those areas which correspond with the powder image on the belt 7, so that it directly visible image or an image made visible by an after-treatment can be obtained on the sheet 16.

The powder present on the belt 7, and occasionally also the powder adhering to the sheet 16, is removed by the elements 19, and 20, respectively, which may consist of a knife, a brush or the like. The latent electrostatic image on the belt 7 is erased by means of the light-source 21. After the belt 7 has passed the guide roller 11, it finally runs through the relaxation device 22 where the photooonductive layer regains its initial sensitivity. An appropriate relaxation device is, e.g., described in particular in the United States Patent 2,919,119.

FIG. 8 represents an embodiment wherein magnetic recording material, e.g., a strip of magnetic tape for an electronic computing apparatus comprising a magnetic recording layer 27 which is coated onto a support 28, is developed with a magnetic attractaole powder such as an iron powder suspension. The magnetic tape containing the powder image 29 is contacted with a thermographic sheet, which is composed of a thin support 30 and a thermosensitive layer 31, in such a way that the thermosensitive layer 31 is turned away from the powder image 29. 'By a short intense infra-red irradiation of the two materials pressed together, a visible reproduction 32 of the recorded magnetic signal on the magnetic tape is obtained in the thermosensitive layer.

FIG. 9 is described later in connection with one of the specific examples;

FIG. 10 illustrates another embodiment of the invention in which the powder image is transferred to an intermediate support before being used to develop the thermosensitive layer. Thus, the powder image 3, after being formed on the photoconductive layer 1 on the support 2 is transferred to an intermediate sheet or support 35, such as paper or the like, by means of any of the known techniques for accomplishing such transfer, as represented by the left side of the figure. Then, the intermediate support 35 bearing the transferred powder image 3 thereon is brought into contact with the thermo-sensitive layers 5 on the support 4 and exposed to infra-red radiation to form the visible image 6 in the thermo-sensitive layer as represented by the right side of the figure.

For executing the present invention, e.g., use can be made of the following materials:

1.ELECTROPHOTOGRAPHIC MATERIAL Electrophotographic material, the photoconductive layers of which are less infra-red absorbing than the developing powders, are, e. g., amorphous selenium, either vacuum deposited or dispersed in a binding agent with high electric resistivity; zinc oxide, dispersed in a binding agent, particularly the layers described in the French patent specification 1,294,375 and the Belgian patent specification 612,102; Zinc sulphide, cadmium sulphide, antimony oxysulphide, sulphur, organic photoconductors especially those described in the French patent specifications 1,254,348, 1,258,844, 1,261,206, 1,271,986 (and its addition 79,705), 1,275,778, 1,285,486, 1,308,762 and 1,310,813.

Polymeric photoconductors in particular those described in the French patent specifications 1,249,634,

,254,024, 1,254,023 and 1,291,570, have the advantage that they can be worked up to self-supporting sheets.

The supports for photoconductive layers can among others be manufactured from opaque or translucent paper or glass; they may be insulating sheets with conductive layers, thin metal sheets, etc.

2.DEVELOPING POWDERS These have to be infra-red absorbing and are preferably non-thermoplastic. Further, depending upon the particular embodiment used, the developing powders have to be magnetic or magnetisable and/or electrosco-pic.

Preferably, the developing powders have a high specific heat and a good head-conductivity. By a non-thermoplastic substance is meant a substance, which at the employed recording temperatures, does not melt nor soften.

As substances which can be used in this respect may be cited:

Carbon in all its various forms, such as anthracite, graphite, carbon black, charcoal, bone black, active coal and organic infra-red absorbing compounds with a high melting point, such as phthalocyanine dyestuffs;

Infra-red absorbing dyestuffs precipitated onto pigments;

Bakelite powder;

Metal powder, such as iron, lead, copper, zinc, silver,

cadmium, aluminum powder;

Metal oxides, such as manganese dioxide, lead oxides,

iron oxides, copper oxide, silver oxide;

Metal sulphides, such as mercury sulphide, cadmium sulphide, molybdenum sulphide.

3.-THERMOSENSITIVE LAYERS Thermosensitive layers comprising the following combinations of thermosensitive substances can successfully be used in the methods according to the present invention.

The following table represents 8 series of combinations of a component A with B and occasionally with C, which give a colored reaction product by heating. For the respective components the temperature is also indicated at which this reaction product and also the color of the reaction product are formed.

Thermosensitive materials, which upon exceeding a critical temperature undergo a visible irreversible change, are very well-known in technical literature.

Thermosensitive materials, which upon exceeding a critical temperature undergo an invisible reversible physi- '3' cal change, are among others described in our French patent specification 1,288,059.

8 After recovering this layer can be used again for a following identical operation.

A Components 13 Quaternary iodide such as;

1. Starch 2. Zinc compoundsuch as:

Zinc ox1de, zinc chloride, zmc

bromide, zinc iodide.

Polyvinyl chloride, chloride Lead stearate Chlorine containing polymer such as:

polyvinylidene copoly[vinyl acetate/vinyl chloride], copolylvinyl chloride/vinyl isooutyl ether], alter chlorinated polyvinyl chloride, chlorinated rubber.

3. p-Phenylenene dlamine Copper stearute 4. Chloranil Antipyrine 5. Iron Dodecyl gallatc 6. Diazonium salt 2,3-dihydroxy-e-sulphonspnthalene 5. Lead acetate C Color of the reaction Color change product temperature B1ue ca.170.

Dark brown to black.... 160-190".

: l-phenyl-3-pyrazo Sodium stearate ca. 70.

Brown In the scope of the invention are included also those therniosensitive materials which upon exceeding a critical temperature are partly reduced to a flowable or meltable condition, allowing the physical transfer of some of their layer substance onto another surface.

The following examples illustrate the present invention.

Example 1 A baryta-coated photographic paper is coated by rollercoating, in such a way that 1 liter covers sq. m. of paper, with a dispersion of a photoconductor and a binding agent which is prepared as follows:

To 1000 cc. of a 4% solution of copoly[vinyl acetate/ vinyl stearate] (85/ in ethanol, 150 g. of zinc oxide, Neige extra pun, type A (marketed by Vieille Montagne S.A., Liege, Belgium), are added whilst thoroughly stirring. Then 10 cc. of a 10% solution of monobutyl phosphate in ethanol are slowly added thereto whilst stirring is continued. This mixture is ground for 24 hr. in a ball mill. Next, 10 cc. of a 10% solution of succinic acid in ethanol and 10 cc. of a 1% solution of Rose Bengale (Cl. 45,440 and 45,435) in ethanol are successively added.

After drying the photoconductive layer is charged to 300 volts/cm. by means of a corona-discharge of -6000 volts and then exposed for 0.7 see. through a diapositive with an incandescent lamp of 75 watts placed at a distance of 10 cm.

The thus obtained latent electrostatic image is made visible by applying thereto an iron powder composed of 99.2% of iron, 0.02% of hydrogen, 0.3% of oxygen, 0.01% of carbon, 0.09% of silicon, less than 0.05% of phosphorus, 0.06% of chromium, 0.26% of manganese, 0.065% of nickel, according to a developing method as described in Electrofax, a New Tool for the Graphic Arts, RCA Laboratories, LB. 1006, November 11, 1955, Fig. 3.

Next, the developed image, in contact with the nontherniosensitive side of a sheet of therrnographic material, containing in its thermosensitive layer as active constituents phenol and an iron salt of one or more higher aliphatic carboxylic acids, e.g., stearic acid, is led whilst exposing to infra-red radiation through an apparatus as, e.g., a Secretary Copying Machine, marketed by Minnesota Mining and Manufacturing Company, St. Paul, Minn, U.S.A., the speed control indicator being set on numeral 2. Due to the selective absorption of the infra-red rays a positive legible image is obtained by col-our change of the thermosensitive material. Up to five good thermographic copies of the same iron powder image can be produced. After use the iron powder is removed with a brush from the photoconductive layer.

To improve the sharpness of the final image, first the latent electrostatic image on the photoconductive layer can be made visible by means of a graphite mixture (size of the particles 0.5 [.L) whereby images with a greater dissolving power are obtained. The further treatment is done as described hereinbefore.

Example 2 In 500 cc. of methylene chloride 150 g. of cop0ly[.N- vinyl carbazole/ethyl acrylate] (60/40) are dissolved.

This solution is diluted with 500 cc. of toluene and as sensitizer 20 cc. of a 10% solution of l-chloroanthraquinone in dimethyl formamide are added. From this solution a thin layer is applied onto a baryta-coated paper support of g./ sq. m. by means of a roller-coating system at a speed of 18 m./min. and in such a way that 1 1.,covers 16.5 sq. m. of paper.

After drying the photoconductive layer is charged to +500 v./cm. by means of a corona-discharge of +6000 volts then exposed for 6 see. through a diapositive with an incandescent lamp of 75 watts placed at a distance of 10cm.

Then the obtained latent electrostatic image is developed by means of an iron powder containing besides iron the following constituents: 0.24% of hydrogen, 2.42% of oxygen, 3.46% of carbon, 0.30% of silicon, 1.10% of phosphorus, 0.045% of chromium, 0.30% of manganese, 0.06% of nickel, and finally the powder image is transferred onto a thermosensitive material and by means of an apparatus (speed control set on 2) as described in Example 1, a thermographic copy of the transferred. powder image is formed. A positive legible image is obtained on the thermosensitive material.

Example 3 A powder image is obtained on an electrophotographic support according to Example 2. With this powder image a duplicating master for the hectographic printing method is prepared in the following way:

The electrophotographic material, consisting of the photoconductive layer 1 and the support 2, is pressed with-its iron powder image 3 against the backing 23 of a commercial carbon paper (FIG. 9) which is little infrared absorbing, the dyestuff layer 24 of which consisting of a wax and a dyestufi such as crystal violet or methylene blue. This little infra-red absorbing dyestuff layer 24 of such a carbon paper is contacted in its turn with a sheet of art printing paper 25.

In passing these contacting sheets between two pressure rollers, they are submitted to an infra-red radiation.

At the place where the greatest part of heat is absorbed, i.e., at the place of the iron powder image, the dyes-tuft layer 24 melts and adheres to the art printing paper. When the sheet of art printing paper 25 is stripped ofl, a positive reversed image 26 from the dyestuff layer of the carbon paper is formed on this sheet.

xample 4 A pergamin paper of 40 g./sq. m. is coated with a photoconductive layer from the following composition:

On the front side:

Copoly[N-vinyl carbazole/ethyl acrylate] (41/59) g 7.5 solution of chloroanthraquinone in dimethyl formamide cc 1 Methylene chloride cc 100 The thickness of this layer is 8 ,Lb.

Onto the rear side, two layers are successively coated:

Layer 1- Stabilized thioacetamide g 3 Sodium stearate g 1 4% solution'of ethyl cellulose in ethanol Layer 2- Lead stearate g 7.5

Titanium dioxide g 6 4% solution of ethyl cellulose in ethanol The front side of the thus obtained material is charge negatively with a corona and then this side is reflectographically exposed for 2 sec. in contact with the original to be copied by means of an incandescent lamp of 100 watts, placed at a distance of 10 cm. Next, said front 2- In 7.5 l. of methanol 610 g. of copoly[vinyl acetate/ vinyl laurate] (80/20) are dissolved. Then 2,250 kg. of zinc oxide Neige extra pur, type A (marketed by Vieille Montagne S.A., Liege, Belgium), are added therea to. This mixture is ground for 24 hr. in a ball mill with porcelain balls. Then whilst thoroughly stirring are successively added:

0.6% solution of monobutyl phosphate in methanol cc 0.6% solution of succinic acid in methanol cc 0.02% solution of Rose Bengale (Cl. 45,440 and Cl. 45,435) in methanol cc With a roller-coating system a thin layer is applied from this composition to a photographic paper support in such a way that 1 1. covers 12 sq. m. of paper.

In the thus obtained sheet of electrophotographic material a latent image is formed by reflectographic exposing to an original having blue, green and red image tones by means of incandescent lamps. Next, the latent image is developed by applying an identical iron powder as used in Example 1. A contrasty powder image with a good grey reproduction of the different colors of the original is obtained.

Then an electrothermographic material is positively charged in order to make a copy of the iron powder image according to the electrothermographic method described in the French patent specification 1,288,059.

The electrothermographic material consists of a per- 10 gamin paper onto which has been coated a layer from a 10% solution of copoly[vinyl chloride/vinyl acetate/ maleic anhydride] (/14/1) in acetone, and a layer from a 5% solution of polyvinyl butyral in a mixture of ethanol and butyl acetate (/10).

This sheet of electrothermographic material is pressed with its rear side against the already developed iron powder image on the sheet of elect-rophotographic material and these sheets pressed together are passed at a speed of 3 cm./sec. before an infra-red lamp General Electric 1000 T3 (1000 watts) placed at a distance of 0.6 cm., the front side of the thermographic material facing the light source.

After separating both materials the iron powder of the electrophotographic material is recovered. Finally, the latent image is developed in the electrother-mographic material containing a powder mixture which consists of 5 g. of a toner, which is described on page 11 of the Belgian patent specification 535,951, and g. of iron filings. After fixing the image by heat a positive blackwhite copy of the colored original is obtained.

Example 6 On an electrophotographic selenium plate, an electrostatic latent reversed image of the original to be copied is formed. The development of the latent reversed image is done by cascade development wherein as color powder Syrischer Asphalt is used.

Next, the thermographic material, as described in Example 1, is pressed with its thermosensitive side against the powder image. The powder image is electrostatically transferred from the selenium plate to the thermographic sheet by means of a corona-discharge on the rear side.

The thermographic sheet with the powder image is then exposed to an infra-red radiation in an apparatus such as a Secretary Copying Machine (see Example 1) the speed control of which is set on 2. By the selective absorption of the infra-red rays in the powder image a positive legible image is obtained by color change of the thermosensitive material.

What we claim is:

1. In a method for the production of copies of an original comprising the steps:

(1) Producing a latent electrostatic image in an insulating photoconductive layer by the steps comprising uniformly applying electrostatic charges to said photoconductive layer and exposing said photoconductive layer to a light image of said original to produce an imagewise pattern of electrostatic charges on said photoconductive layer;

(2) Developing said latent electrostatic image on said photoconductive layer with free-flowing infra-red absorbing powder particles that remain in powder form upon exposure to heat;

(3) Contacting said photoconductive layer carrying said powder image with a thermographic copy sheet having a therrno-sensitive layer of substantially less infra-red absorptivity than said powder particles, said thermo-sensitive layer benig adapted to undergo an irreversible change in appearance upon exposure to heat;

(4) Exposing said photoconductive layer and copy sheet to infra-red radiation to produce said irreversible change in said thermosensitive layer in correspondence with a heat pattern produced by infrared radiation absorption by said powder image, while said thermo-sensitive layer is in contact with said powder image;

(5) Separating said photoconductive layer and said copy sheet; and

(6) Removing the powder particles from said layers.

2. The method of claim 1, wherein the thermo-sensitive layer as a result of heating undergoes an invisible change that is later developed to produce a visible image.

3. In a method for the production of copies of an original Comprising the steps:

(1) Producing a latent electrostatic image in a com posite copy sheet having an insulating photoconductive layer and a thermosensitive layer arranged in integral relationship, said thermosensitive layer being adapted to undergo an irreversible change in appearance upon exposure to heat, by the steps comprising uniformly applying electrostatic charges to said photoconductive layer and exposing said photo- .conductive layer to a light image of said original to produce an i-magewise pattern of electrostatic charges on said photoconductive layer;

(2) Developing said latent electrostatic image on said photoconductive layer with freedlowin g infra-red absorbing powder partioles that remain in powder form upon exposure to heat, said particles having a substantially higher infra-red absorptivity than said thermosensitive layer;

(3) Exposing said layers to infra-red radiation to produce said, irreversible change in said thermosensitive layer in correspondence with a heat pattern produced by infra-red radiation absorption by said powder image; and

(4) Removing the powder particles from said copy sheet.

4. The method as in claim 3 wherein said photoconductive layer is provided on one side of an electrically conductive backing and said thermosensitive layer on the other side of said backing.

5. The method of claim 3 wherein said powder image is formed directly on said thermosensitive layer so as to be in contact therewith.

6. In a method for the production of copies of an original comprising the steps:

(1) Producing a magnetic pattern in a magnetizable layer by selectively magnetizing areas of said magnetizable layer in accordance with an image of said original;

(2) Developing said magnetic pattern on said magnetizable layer with free-flowing infra-red absorbing magnetically permeable powder particles that remain in powder form upon exposure to heat;

(3) Contacting said magnetizable layer carrying said powder image with a thermographic copy sheet having a therrno-sensitive layer of substantially less infra- .red absorptivity than said powder particles, said thermo-sensitive layer being adapted to undergo an irreversible change in appearance upon exposure to heat;

(4) Exposing said magnetizable layer and copy sheet to infra-red radiation to produce said irreversible change in said thermo-sensitive layer in correspondence with a heat pattern produced by infra-red radiation absorption by said powder image, while said thermo-sensitive layer is in contact with said powder ma (5 Separating said magnetizable layer and said copy sheet; and

(6) Removing the powder particles from said layers.

7. In a method for the production of copies oran original comprising the steps:

( 1) Producing a latent electrostatic image in an insulating photoconductive layer by the steps comprising uniformly applying electrostatic charges to said photoconductive layer and exposing-said photoconductive layer to a light image of said original to produce an image-wise pattern of electrostatic charges on said photoconductive layer; 1

(2) Developing said latent electrostatic image on said photoconiductive layer with free-flowing infra-red absorbing powder particles that remain in powder form upon exposure to heat;

(3) Transferring the thus-formed powder image from said photoconductive layer onto one surface of a thermographic copy sheet having a thermo-sensitive layer of substantially less infra red absorptivity than said powder particles, said thermo-sensitive layer being adapted to undergo an irreversible change in appearance upon exposure to heat;

(4) Exposing said copy sheet to infra-red radiation to produce said irreversible change in said thermo-sem sitive layer in correspondence with a heat pattern produced by infra-red radiation absorption by said powder image while said powder image is disposed on said copy sheet surface; and

(5) Removing the powder particles from said copy sheet surface.

8;. In a method for the production of copies of an original comprising the steps:

(1) Producing a latent electrostatic image in an insulating photoconductive layer by the steps comprising uniformly applying electrostatic charges to said p-hotoconductive layer and exposing said photoconductive layer to a light image of said original to produce an image-wise pattern of electrostatic charges on said photoconductive layer;

(2) Developing said latent electrostatic image on said photocondnctiwe layer with free-flowing infra-red absorbing powder particles that remain in powder form upon exposure to heat;

(3) Transferring the thus-formed powder image into an intermediate support;

(4) Contacting said intermediate support carrying said powder image with a thermographic copy sheet having a thermo-sensitive layer of substantially less infra-red absorptivity than said powder particles, said t-hermo-sensitive layer being adapted to undergo an irreversible change in appearance upon exposure to heat;

(5) Exposing said intermediate support and copy sheet to infra-red radiation to produce said irreversible change in said therrno-sensitive layer in correspondence with a heat pattern produced by infra-red radiation absorption by said powder image, while said therrno-sensitivc layer is in contact with said powder image;

( 6) Separating said intermediate support and said copy sheet; and

(7) Removing the powder particles from said support and thermo-sensitive layer.

References Cited by the Examiner UNITED STATES PATENTS 2,713,822 I 7/1955 Newman 117.36.3 2,855,324 10/1958 Van Dorn.

2,884,343 I 4/ 19'59 Kulesza. 3,054,692 9/1962 Newman et al. 250-65 3,086,113 4/1963 McNaney 25049.5 3,119,014 1/1964 Newman t 25065 FOREIGN PATENTS 722,023 1/1955 Great Britain.

RALPH G. NI LSON, Primary Examiner.

W. F. LINDQUIST, Assistant Examiner. 

1. IN A METHOD FOR THE PRODUCTION OF COPIES OF AN ORIGINAL COMPRISING THE STEPS: (1) PRODUCING A LATENT ELECTROSTATIC IMAGE IN AN INSULATING PHOTOCONDUCTIVE LAYER BY THE STEPS COMPRISING UNIFORMLY APPLYING ELECTROSTATIC CHARGES TO SAID PHOTOCONDUCTIVE LAYER AND EXPOSING SAID PHOTOCONDUCTIVE LAYER TO A LIGHT IMAGE OF SAID ORIGINAL TO PRODUCE AN IMAGEWISE PATTERN OF ELECTROSTATIC CHARGES ON SAID PHOTOCONDUCTIVE LAYER; (2) DEVELOPING SAID LATENT ELECTROSTATIC IMAGE ON SAID PHOTOCONDUCTIVE LAYER WITH FREE-FLOWING INFRA-RED ABSORBING POWDER PARTICLES THAT REMAIN IN POWDER FORM UPON EXPOSURE TO HEAT; (3) CONTACTING SAID PHOTOCONDUCTIVE LAYER CARRYING SAID POWDER IMAGE WITH A THERMOGRAPHIC COPY SHEET HAVING A THERMO-SENSITIVE LAYER OF SUBSTANTIALLY LESS INFRA-RED ABSORPTIVITY THAN SAID POWDER PARTICLES, SAID THERMO-SENSITIVE LAYER BEING ADAPTED TO UNDERGO AN IRREVERSIBLE CHANGE IN APPEARANCE UPON EXPOSURE TO HEAT; (4) EXPOSING SAID PHOTOCONDUCTIVE LAYER AND COPY SHEET TO INFRA-RED RADIATION TO PRODUCE SAID IRREVERSIBLE CHANGE IN SAID THERMOSENSITIVE LAYER IN CORRESPONDENCE WITH A HEAT PATTERN PRODUCED BY INFRARED RADIATION ABSORPTION BY SAID POWDER IMAGE, WHILE SAID THERMO-SENSITIVE LAYER IS IN CONTACT WITH SAID POWDER IMAGE; (5) SEPARATING SAID PHOTOCONDUCTIVE LAYER AND SAID COPY SHEET; AND (6) REMOVING THE POWDER PARTICLES FROM SAID LAYERS. 